mete, anybody in their right mind who has access to a rifle or shotgun will use that over a handgun in the vast majority of confrontations; if barrier penetration is a concern, the rifle is obviously the better choice.
So what? Pistol rounds will still go through sheet metal without much difficulty. If you get lucky, the round catches a reinforcing beam, power window drive motor, etc; if not, odds are even a .22 is going through the door or fender.
So, can some parts of a car provide "cover"? Yes. Do most parts of a car provide cover? No, most parts of the car provide concealment, as has been explained in this thread and in the previous one about this topic.
Concealment is often better than no concealment, but sometimes maneuver is the better option. The situation will vary. Generally, though, most other large objects encountered in a city (or rural road) provide much better protection than does a car.